In a conventional electrochemical biosensor, a measuring method has been mainly used in which a voltage is applied to an electrode system and a Cottrell current resulting from the diffusion of a substance is measured. For example, Patent Document 1 describes a measuring method in which an oxidizing agent and a buffering agent are incorporated in a reaction system; a reaction is allowed to proceed until the reaction is substantially completed; and then a potential is applied between electrodes and a sample, to measure the Cottrell current. The Cottrell current, represented by the Cottrell equation (the following Equation (1)), is a current which depends on the diffusion of a substance, and is characterized by including a diffusion coefficient (D) of the substance. In terms of reaction kinetics, it can be said to be a diffusion-limiting state.
                    i        =                                                            nFAC                0                0                            ⁢                              D                0                                  1                  /                  2                                                                                    π                                  1                  /                  2                                            ⁢                              t                                  1                  /                  2                                                              =                      Kt                          ⋒                              1                /                2                                                                        (        1        )            i: Current (A)n: Reaction electron number (eq/mol)F: Faraday constant (96,485 C/eq)A: Electrode surface area (cm2)CO: Concentration of 0 (mol/cm3)DO: Diffusion coefficient of 0 (cm2/s)T: Time (s)
In Patent Document 2, microelectrodes are used in the measurement of an analyte in a microfluid, and measurement conditions which depend on the diffusion coefficient (D) of the analyte are disclosed.
Further, Patent Document 3 describes the Cottrell equation and the diffusion coefficient (D), and discloses an example in which the diffusion coefficient is calculated based on an experiment.
In addition, Patent Document 4 describes a step of applying a potential between electrodes such that the potential of a working electrode determines the diffusion rate of redox species.